Many active substances need to be delivered topically, whether to human or animal skin (for instance, in the case of pharmaceutically active substances or cosmetics) or to an inanimate surface (for example, disinfectants and other household products, paints, varnishes, adhesives and the like). Such substances need to be formulated in a vehicle which is suitable both for their storage prior to use and for their subsequent topical delivery.
For some such products, it can be desirable to protect the active substance from environmental effects such as heat, moisture or in particular light or oxygen. Instead or in addition, such products may include volatile ingredients such as fragrances, the release of which may need to be minimised during periods of non-use.
Such aims can be achieved in part by encapsulating the relevant substance(s) in delivery vehicles such as liposomes or microcapsules. The preparation of such active-loaded delivery systems can often be complex, time consuming and expensive however. Problems can arise in ensuring that the encapsulating entities are sufficiently uniform in size and shape to ensure the resultant formulation meets quality control and regulatory standards and to provide homogeneity in active substance concentration. It can also be difficult to achieve adequately high active substance loadings in the encapsulating entities, without making those entities relatively large in size and in turn compromising the physical properties of the overall formulation.
It is moreover necessary in topical formulations to ensure that any encapsulated substances can be released to an adequate extent on application to the intended surface.
This is not always straightforward if the substance is also to be sufficiently well encapsulated as to protect it prior to the point of use.
From WO-2005/000280 it is known to use the exine coatings of naturally derived (typically plant) spores as delivery vehicles for pharmaceutical and dietetic substances. These coatings can be isolated from spores by successive treatments with organic solvents, alkali and acid so as to remove the lipid, carbohydrate, protein and nucleic acid components that may be attached to or contained within the exine shell. Enzymic methods have also been used to isolate the exine coating from other components of the spore.
Exine coatings take the form of essentially hollow capsules which can be impregnated or filled with, or chemically or physically bound to, another substance, for example as described in WO-2005/000280. They are known to be chemically and physically extremely stable.
The formulations disclosed in WO-2005/000280 are all pharmaceutical or dietetic dosage forms which are intended for systemic delivery, primarily oral or pulmonary although mention is also made of dermal and transdermal administration. The active ingredient is released when the exine is broken down, biochemically, within the body. In other words, these dosage forms are intended for absorption into the bloodstream followed by degradation of the exine coating to liberate the associated active substance. Such a release mechanism is clearly not suitable for local delivery of a substance. Where topical delivery is mentioned in WO-2005/000280, this is therefore in the context of transdermal delivery of systemic active substances.
It is an aim of the present invention to provide novel active substance-containing formulations which can help to provide an appropriate degree of protection for the active substance whilst also helping to achieve an appropriate degree of local release of the substance on topical administration.